THVD8010: THVD8000 common mode noise immunity

Hi,

How long is the 18AWG cable in your application? In general I would suggest using THVD8010 (with higher RX threshold) in a harsh noisy environment. From common mode point of view, I think using the devices single-ended would be similar as using them differentially, since the current return path is the other wire.

Regards,

Hao

Hi Hao,

Thanks for your fast answer. We are planning to use THVD8010 yes. The distance cable distance can be between 50m-200m maximum. I have included 3 solutions that I'm evaluating at the moment. Solution #1, that is full differential circuitry with the return path on the "B" wire. Solution #2, where I could use the electrical Ground for the return Path and Solution #3 in single-ended and use the "B" wire as return path. On solution #3, the GND of the transceiver is wired directly from LDO/Transceiver on the end point to the start point without any Capacitor/Inductor added to the wire, so It could be the solution with the lowest common-mode noise in my understanding ?

Hi,

Thanks for the diagrams, which make the discussion much easier. I think the best solution depends on the nature of the noise source. If the noise is truly common mode (same amount of energy coupled to two wires), the concern of solution #3 is that the ground and Vbb wires may have different impedance. Therefore it's possible that the voltage changes less on the ground wire and more on the Vbb. If that's the case, the noise could become signal ended that beats the purpose of differential signaling. On top of the noise coupled to the bus, the common mode noise could also come from different grounding. However since the ground of two sides are shared, I assume the solution #1 and #2 would have similar performance.  

Regards,

Hao      

Hi,

    Thanks for your answer. Since the electrical ground return path is resistive and can carry a lot of noise in my application, then I suppose that solution #1 would be the best solution. With this solution, my product will be completely isolated for the electrical ground, so less common-mode noise. The product will then be "Isolated" from the ground noise because of the 18AWG shielded twisted-pair. I also have another application were I can't have any twisted-pair and I'm forced to use 18AWG wire non-twisted together, but within the same cable jacket (so very close together). Since my communication speed and Carrier frequency are quite-low (9,600bauds and 125,000Hz), should I be worried about the differential noise within this kind of installation with the solution #1? Do I need a termination resistor ?

Best regards

Vincent

Hi Hao,

   When this situation happen, the number of node would be lower than 10

Vincent

Vincent,

Please keep the nodes close to the main bus, which will help reduce the settling time.

Regards,

Hao

Thanks for your help !

Vincent